package com.xsoft.web.util;

import java.io.Serializable;
import java.net.InetAddress;
import java.util.concurrent.locks.ReentrantLock;

import org.hibernate.util.BytesHelper;

public class IDHexGenerator {
	private static final int IP;
	static {
		int ipadd;
		try {
			ipadd = BytesHelper.toInt( InetAddress.getLocalHost().getAddress() );
		}
		catch (Exception e) {
			ipadd = 0;
		}
		IP = ipadd;
	}
	private static short counter = (short) 0;
	private static final int JVM = (int) ( System.currentTimeMillis() >>> 8 );
	private static ReentrantLock countLock = new ReentrantLock();
	
	private static String format(int intval) {
		String formatted = Integer.toHexString(intval);
		StringBuffer buf = new StringBuffer("00000000");
		buf.replace( 8-formatted.length(), 8, formatted );
		return buf.toString();
	}

	private static String format(short shortval) {
		String formatted = Integer.toHexString(shortval);
		StringBuffer buf = new StringBuffer("0000");
		buf.replace( 4-formatted.length(), 4, formatted );
		return buf.toString();
	}

	public static Serializable generateID() {
		return new StringBuffer(36)
			.append( format( getIP() ) )
			.append( format( getJVM() ) )
			.append( format( getHiTime() ) )
			.append( format( getLoTime() ) )
			.append( format( getCount() ) )
			.toString();
	}
	
	public static Serializable generateID(String sep) {
		return new StringBuffer(36)
			.append( format( getIP() ) ).append(sep)
			.append( format( getJVM() ) ).append(sep)
			.append( format( getHiTime() ) ).append(sep)
			.append( format( getLoTime() ) ).append(sep)
			.append( format( getCount() ) )
			.toString();
	}
	
	/**
	 * Unique across JVMs on this machine (unless they load this class
	 * in the same quater second - very unlikely)
	 */
	private static int getJVM() {
		return JVM;
	}

	/**
	 * Unique in a millisecond for this JVM instance (unless there
	 * are > Short.MAX_VALUE instances created in a millisecond)
	 */
	private static short getCount() {
		countLock.lock();
			if (counter < 0) counter = 0;
			counter++;
		countLock.unlock();
		return counter;
	}

	/**
	 * Unique in a local network
	 */
	private static int getIP() {
		return IP;
	}

	/**
	 * Unique down to millisecond
	 */
	private static short getHiTime() {
		return (short) ( System.currentTimeMillis() >>> 32 );
	}
	private static int getLoTime() {
		return (int) System.currentTimeMillis();
	}
}
